1. Field of the Invention
The present invention relates to a movable carriage, and particularly to a movable carriage that is moved to a hospital room with an X-ray imaging apparatus mounted thereon for taking an X-ray photography.
2. Description of the Related Art
A movable carriage of this type generally has wheels on a front and rear of a carriage body. The wheels include wheels that can freely steer (i.e., can change a moving direction of the carriage) and wheels that cannot steer. Examples of the combination of wheels in a movable carriage include, a movable carriages in which the front wheels can freely turn and the rear wheels cannot freely steer, a movable carriage in which the front wheels cannot freely steer and the rear wheels can freely steer, and a movable carriage in which the front and rear wheels can freely steer.
Japanese Patent Application Laid-Open No. 2001-309910 discusses a carriage that includes front wheels that can freely steer, and rear wheels that cannot be steered, and has an X-ray control unit mounted thereon. This carriage can move forward or backward with a drive motor by an operation of a lever handle.
Japanese Patent Application Laid-Open No. 10-203401 discusses a steering switching carriage having a steering switching mechanism that can switch a “front/rear wheels steerable operation” and an “operation of fixing rear wheels in straight moving direction and freely steering front wheels”.
Japanese Patent Application Laid-Open No. 6-92259 discusses a four-wheel steering control apparatus that causes phases of front and rear wheels to be the same as each other in a region where a steering angle is a predetermined value or smaller, and changes the steering angle of the rear wheels to cause the phase of the rear wheels to be opposite to the front wheel in a region where the steering angle is a predetermined steering angle or larger.
Desired traveling performance of a carriage is different depending upon a travelling place or condition. Specifically, on a straight corridor, the carriage is required to travel with excellent straight-line stability according to an operator's pushing and pulling operation of the carriage. When there is an obstacle in the traveling direction, the carriage desirably moves to the right or to the left with the direction of the carriage body being maintained according to an operation of changing its course to the right or to the left by the operator. When steering a corner, the carriage desirably moves with excellent steering performance without a collision between the carriage body and the corner or wall due to inner/outer wheel difference.
However, the movable carriage discussed in Japanese Patent Application Laid-Open No. 2001-309910 cannot keep the direction of the carriage body when an operator tries to change its course during the movement in a straight line, since the carriage is configured in such a manner that the front wheel can freely steer, and the rear wheel cannot steer. When turning the corner, the carriage generates inner/outer wheel difference.
The carriage discussed in Japanese Patent Application Laid-Open No. 10-203401 does not have a grip unit. Therefore, it cannot keep up with the operation of pushing or pulling the carriage by the operator. The carriage is configured in such a manner that the rear wheel has the phase opposite to the phase of the front wheel, or is fixed in the straight moving direction. Therefore, the carriage cannot keep the direction of the carriage body when the operator tries to change its course during the movement in a straight line.
The four-wheel steering control apparatus discussed in Japanese Patent Application Laid-Open No. 6-92259 changes a steering angle to a steering operation of a driver. It cannot keep up with the operation of pushing or pulling the carriage by the operator.